Portable generators for producing electricity are well known and have been commercially available for many years. These devices typically include an internal combustion engine, are designed to generate sufficient electrical power to run one or more common household or commercial electronic devices, and typically use gasoline as fuel. They are adapted to provide alternating current (AC) electricity, through a standard two-prong or three-prong plug receiver, at 120 or 240 volts, and at 50 to 60 Hz; also common is an additional 12 volt DC power port for charging lead acid batteries. Many of these devices are not fuel injected and include a carburetor and a manual choke. The carburetor mixes the fuel with air before it enters the cylinder. When the engine is first started (cold start), the choke is pulled out (air restricting) to minimize the amount of air mixed with the fuel, so that the cold fuel will combust properly; when the engine warms, the choke is pushed in (air non-restricting) so that the correct amount of air is mixed with fuel for proper combustion at the steady state operating temperature.
Some of the smallest commercially available portable generators include the YAMAHA Inverter EF1000iS and the HONDA EU1000i. The capacity of the fuel tanks in these types of devices is about 0.6 gallons of gasoline, allowing operation at the maximum load of around 1000 W of 4 to 6 hours, or at ¼ load for 8 to 12 hours. These generators produce less noise than larger models, having a typical sound output of 47 to 59 dB. These devices include an internal combustion engine using gasoline fuel, so they necessarily generate carbon monoxide (CO), and do not come equipped with a catalytic converter or CO safety shut down features. Thus the manufactures strongly discourage indoor use because of the danger of carbon monoxide poisoning to humans and animals. Furthermore, the exhaust gases are hot and all metal parts of the device which come into contact with the exhaust gasses also become dangerously hot.
There has been a proliferation of small portable electronic devices in recent years, most of which include small rechargeable batteries. Examples include laptop computers, mobile telephone, personal digital assistants, portable digital cameras and global positioning systems. The rechargeable batteries are most commonly lithium ion batteries, although other varieties are available. The small portable electronic devices typically include a removable power cord with a standard two-prong or three-prong plug, or a universal serial bus (USB) plug, for plugging into a corresponding plug receiver, which allows for recharging the rechargeable batteries. Also commonly available are removable power cords with a standard cigarette lighter plug, for recharging the rechargeable batteries using a cigarette lighter plug receiver in an automobile or other vehicle.
For field operation by consumers of portable appliances such as televisions and radios, and small portable electronic devices and recharging of the batteries therein, portable generators have come into common use. Although an automobile is used to get to the field location for camping or tailgating, and is therefore available for recharging batteries or for providing DC power, unless the engine and alternator are running there is a risk of draining the automobile battery, and compromising the operation or starting capacity of the automobile. If the engine is running, over extended periods of time, there will be substantial use of the gasoline from the fuel storage tank, far in excess of the amount of electricity needed to recharge batteries for small portable electronic devices. This results because the rechargeable batteries require a specific amount of time and power to recharge, and even when just idling the vehicle engine consumes far more fuel than necessary to recharge the batteries. The advantage of using a portable generator is the much greater efficiency for generating the amount of electricity needed to recharge batteries, over the period of time necessary for recharging, as compared to an automobile engine. In other words, there is a superior match between the power generation and the power consumption. Gasoline for the generator is readily available at retail gasoline refueling stations.
Often, remote field location operations are staged, first setting up a base camp, next a remote camp, and lastly individuals on foot or with only a single vehicle are sent even farther afield. Remote field location operations are therefore required to carry all supplies, especially consumable supplies, which will be needed. Not only is the total amount of supplies often minimized to reduce cost and weight, but the variety of supplies is also minimized, to reduce logistical costs and complexity in transporting materials to, and resupplying, the base camp.
To get to remote field locations, such as those in wilderness areas far away from highways, vehicles which use diesel fuel, rather than gasoline are commonly used. The supplies carried to such remote field locations only include diesel fuel, not gasoline, for the vehicles. In these cases, recharging of batteries is carried out using power generated by the vehicle, keeping the vehicle engine running while recharging the batteries or from a large 2-10 kW diesel generator carried by the vehicle. As noted above, a vehicle engine and alternator is especially inefficient for recharging small batteries. Furthermore, in these remote field locations, the noise generated by the vehicles engine or diesel generator can be especially undesirable, considering the extended period of time needed for recharging batteries. Lastly, unless constantly monitored the vehicle engine or diesel generator will continue running even if the batteries have completed recharging, continuing the consumption of diesel fuel until human intervention or until all of the fuel is consumed. Under these circumstances, the use of diesel fuel and a generator or vehicle engine vehicle alternator is particularly inefficient for recharging small batteries.
To address this inefficient use of diesel fuel in remote field location operations, other energy sources have been used, but each suffers from drawbacks. Solar power units are available, but they tend to be large and require significant set up time to spread out the solar cells for sufficient energy generation. Furthermore, sun light is only available during the day, and unpredictable cloud cover can make the availability of solar power unreliable and intermittent over the time scale of remote field location operations. Wind power is potentially available night and day, but otherwise can require similarly bulky equipment and can be similarly unreliable and intermittent. Finally, for some remote field location operations, such as during extreme weather conditions, it is required to keep all supplies and equipment indoors; neither solar power nor wind power is available indoors, and running the engine of a diesel engine indoors is too dangerous due to carbon monoxide accumulation from the engine exhaust.
In order to address the needs of remote field location operations for small amounts of electrical power over an extended period of time for both the operation of, and recharging of batteries within, small portable electronic devices, small portable generators including an internal combustion engine was considered. However, such devices still suffer from many of the disadvantages of using a vehicle engine or large diesel generator. Although less noisy, they nonetheless generate significant amounts of noise. Furthermore, indoor operation is also dangerous due to exhaust gases containing carbon monoxide. Although the use of fuel over any specific period of time is less, the small portable generators still continue to run when recharging of batteries is completed unless constantly monitored. A further disadvantage is that an additional fuel, such as gasoline, is needed since small portable generators typically do not use the same fuel as diesel vehicles, complicating the supply logistics by adding to the total amount and variety of materials.